[LAU] Using linux-rt with Ati Mobility X700

I hadn't got the time to do some music on my ubuntu machine the last few months, but yesterday I wanted to boot the rt-kernel on my machine. To my surprise, I only got a resolution of 800x600. I used to have the proprietary driver from ati.com installed; Though this one doesn't work on the Linux-rt kernel (no 3D acceleration), I used to get the desired resolution of 1400x1050. To regain this resolution, I tried several xorf.conf files, using "ati", "fglrx" and "vesa" as driver, but none worked. (In the process of doing so, I somehow even managed to screw up my Internet configuration on the main kernel (d'oh), so I'm actually writing this on 800x600... ) So my question is: Is there actually someone on this list, who is able to boot Linux-rt on his ubuntu machine, using an ati x700 mobility? I'd really appreciate any suggestions, more so working xorg.conf files and verified driver numbers. Greetings from Euskirchen Matthias